1. Field
This following description relates to a pseudo-orthogonal code generator, and more particularly, to a pseudo-orthogonal code generator that minimizes the complexity of a pseudo-orthogonal code generator and improves the operating speed in a radio transmitting system using pseudo-orthogonal codes.
2. Description of the Related Art
Table 1 is a Walsh-Hardamard code table that is used in a conventional orthogonal coding method. For example, in a conventional orthogonal code generator receiving four binary signal inputs, the total number of orthogonal codes that a bit row can have from these inputs are 16(=24). In this example, the length of each orthogonal code is always 16 bits as shown in Table 1, and each column of the orthogonal codes are orthogonal to each other.
TABLE 1WALSH-HARDAMARD CODE TABLE WalshWalsh codeNo.01234567891011121314150000000000000000010101010101010101200110011001100113011001100110011040000111100001111501011010010110106001111000011110070110100101101001800000000111111119010101011010101010 001100111100110011 011001101001100112 000011111111000013 010110101010010114 001111001100001115 0110100110010110
As described above, a conventional orthogonal code generator requires 16 code bits for transmission of total 4 bits. Thus, the efficiency of the transmission channel is deteriorated due to an extremely low spectral efficiency of no more than 0.25(4/16).
Korean Patent No. 0761669, issued on Sep. 19, 2007, describes a pseudo-orthogonal code generator having better spectral efficiency than a conventional orthogonal code generator.
In the pseudo-orthogonal code generator described in Korean Patent No. 0761669, the contents of the pseudo-orthogonal code memory, for example, the relationship between the input address and the output code, may be expressed by Equation 1.
                              C          ⁡                      (            i            )                          =                  0.5          ×                      {                                                                                                      (                                              -                        1                                            )                                                                                      b                        2                                            ⊕                                              (                                                                              i                            1                                                    ⁢                          Λ                          ⁢                                                                                                          ⁢                                                      b                            1                                                                          )                                            ⊕                                              (                                                                              i                            0                                                    ⁢                          Λ                          ⁢                                                                                                          ⁢                                                      b                            0                                                                          )                                                                                                                                                              +                                                                  (                                                  -                          1                                                )                                                                                              b                          5                                                ⊕                                                  i                          2                                                ⊕                                                  (                                                                                    i                              1                                                        ⁢                            Λ                            ⁢                                                                                                                  ⁢                                                          b                              4                                                                                )                                                ⊕                                                  (                                                                                    i                              0                                                        ⁢                            Λ                            ⁢                                                                                                                  ⁢                                                          b                              3                                                                                )                                                                                                                                                                                      +                                                                  (                                                  -                          1                                                )                                                                                              b                          8                                                ⊕                                                  i                          3                                                ⊕                                                  (                                                                                    i                              1                                                        ⁢                            Λ                            ⁢                                                                                                                  ⁢                                                          b                              7                                                                                )                                                ⊕                                                  (                                                                                    i                              0                                                        ⁢                            Λ                            ⁢                                                                                                                  ⁢                                                          b                              6                                                                                )                                                                                                                                                                                      +                                                                  (                                                  -                          1                                                )                                                                                                                                                        b                              2                                                        ⊕                                                          b                              5                                                        ⊕                                                          b                              8                                                                                _                                                ⊕                                                  i                          3                                                ⊕                                                  i                          2                                                ⊕                                                  (                                                                                    i                              2                                                        ⁢                                                          Λ                              ⁡                                                              (                                                                                                      b                                    1                                                                    ⊕                                                                      b                                    4                                                                    ⊕                                                                      b                                    7                                                                                                  )                                                                                                              )                                                ⊕                                                  (                                                                                    i                              0                                                        ⁢                                                          Λ                              ⁡                                                              (                                                                                                      b                                    0                                                                    ⊕                                                                      b                                    3                                                                    ⊕                                                                      b                                    6                                                                                                  )                                                                                                              )                                                                                                                                                                            Equation        ⁢                                  ⁢        1            
Using the pseudo-orthogonal code generator of Korean Patent No. 0761669, the spectral efficiency becomes 0.5625(9/16) by converting a 9-bit size transmission information data into a pseudo-orthogonal code in accordance with Walsh-Hadamard code table as shown in Table 1. Thus, the spectral efficiency is enhanced by 225% in comparison to the conventional orthogonal code generator.
However, the pseudo-orthogonal code generator of Korean Patent No. 0761669 requires four multiplexers and three adders in addition to a 9-bit serial-to-parallel converter, a 512×16-bit ROM, and a 1-bit parallel-to-serial converter. Thus, the configuration is very complicated and the overall size becomes larger due to the much enlarged gate area when the pseudo-orthogonal code generator is fabricated as an application specific integrated circuit (ASIC). In addition to the above problem, there is a disadvantage of a slower operating speed because it uses a ROM.